Mariager Fjord is a highly eutrophicated estuary and is considered to have a bad water quality according to the Aquatic Plan 1.3 [2011] for Mariager Fjord. This is caused by a high nitrogen and phosphorus load into the fjord from the adjacent streams. The Water Framework Directive [2000] states that all European water bodies must reach a good water quality at the end of 2015. In this report, the nutrient reduction is going to be investigated by setting up an ecological model and a hydrodynamic model. Furthermore, the behaviour of the ecological model is going to be observed in regards to the nutrient reductions. In order to improve the water quality of the fjord, a conceptual solution is going to be studied. Although nitrogen reduction can be achieved by implementing the suggested solutions, the criteria for the end of 2015 cannot be complied in time. It is possible though that a good water quality can be reached in the near future.